Iron Tetrasulfonatophthalocyanine-Catalyzed Starch Oxidation Using H2O2:Interplay between Catalyst Activity, Selectivity, and Stability

Oxidized starch can be efficiently prepared using H2O2 as an oxidant and iron(III) tetrasulfophthalocyanine (FePcS) as a catalyst, with properties in the same range as those for commercial oxidized starches prepared using NaOCl. Herein, we performed an in-depth study on the oxidation of potato starch focusing on the mode of operation of this green catalytic system and its fate as the reaction progresses. At optimum batch reaction conditions (H2O2/FePcS molar ratio of 6000, 50 °C, and pH 10), a high product yield (91 wt %) was obtained with substantial degrees of substitution (DSCOOH of 1.4 and DSCO of 4.1 per 100 AGU) and significantly reduced viscosity (197 mPa·s) by dosing H2O2. Model compound studies showed limited activity of the catalyst for C6 oxidation, indicating that carboxylic acid incorporation likely results from C-C bond cleavage events. The influence of the process conditions on the stability of the FePcS catalyst was studied using UV-vis and Raman spectroscopic techniques, revealing that both increased H2O2 concentration and temperature promote the irreversible degradation of the FePcS catalyst at high pH. The rate and extent of FePcS degradation were found to strongly depend on the initial H2O2 concentration where also the rapid decomposition of H2O2 by FePcS occurs. These results explain why the slow addition of H2O2 in combination with low FePcS catalyst concentration is beneficial for the efficient application in starch oxidation

Manganese catalysts in homogeneous oxidation reactions

Veel essentiële functies in organismen worden vervuld door enzymen die mangaan bevatten. Enzymen zijn verbindingen die (bio)chemische reacties katalyseren en tijdens de omzetting van de uitgangsstoffen (substraten) verandert de katalysator (het enzym) niet. Efficiënte katalysatoren kunnen in zeer kleine hoeveelheden een uitgangstof volledig omzetten tot het gewenste product. ... Zie: Samenvatting

Benign catalytic oxidation of potato starch using a homogeneous binuclear manganese catalyst and hydrogen peroxide

Oxidation is an excellent way to improve the properties of native starches. After oxidation, products are easier to handle due to a lowered paste viscosity in water, an improved stability and enhanced adhesive properties. Currently, oxidation by sodium hypochlorite (NaOCl) is the dominant commercial process for oxidized starches, which allows for oxidation of hydroxyl groups into carboxylic acids. Here, we show that by using a commercial homogeneous binuclear manganese catalyst ([MnIV2(μ-O)3(tmtacn)2][(CH3COO)2] (Mncat), with tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), and H2O2 as oxidant, starch can be oxidised without the cogeneration of ecotoxic chlorinated waste products. Although oxidation with H2O2 and other catalysts (mainly iron-based) has been done, high loadings were needed and the starch pasting properties were not yet on par with NaOCl oxidised starches. Starch granules suspended in water can be oxidized at room temperature with 0.0021 mol% Mncat and 1 wt% H2O2 yielding starch with similar properties (DSCOOH, yield, pasting properties) as those achieved by NaOCl oxidation. This catalytic oxidation of starch with an earth-abundant metal catalyst at ppm loadings, which is widely applied in detergents, highlights the potential for the development of a more sustainable process to produce oxidized starches

Mechanism of Cis-Dihydroxylation and Epoxidation of Alkenes by Highly H2O2 Efficient Dinuclear Manganese Catalysts

In the presence of carboxylic acids the complex [MnIV2(µ-O)3(tmtacn)2]2+ (where tmtacn = N,N',N"-trimethyl-1,4,7-triazacyclononane) is shown to be highly efficient in catalyzing the oxidation of alkenes to the corresponding cis-diol and epoxide with H2O2 as terminal oxidant. The selectivity of the catalytic system with respect to (w.r.t.) either cis-dihydroxylation or epoxidation of alkenes is shown to be dependent on the carboxylic acid employed. High turnover numbers (t.o.n. > 2000) can be achieved especially w.r.t. cis-dihydroxylation for which the use of 2,6-dichlorobenzoic acid allows for the highest t.o.n. reported thus far for cis-dihydroxylation of alkenes catalyzed by a first-row transition metal and high efficiency w.r.t. the terminal oxidant (H2O2). The high activity and selectivity is due to the in situ formation of bis(µ-carboxylato)-bridged dinuclear manganese(III) complexes. Tuning of the activity of the catalyst by variation in the carboxylate ligands is dependent on both the electron-withdrawing nature of the ligand and on steric effects. By contrast, the cis-diol/epoxide selectivity is dominated by steric factors. The role of solvent, catalyst oxidation state, H2O, and carboxylic acid concentration and the nature of the carboxylic acid employed on both the activity and the selectivity of the catalysis are explored together with speciation analysis and isotope labeling studies. The results confirm that the complexes of the type [Mn2(µ-O)(µ-R-CO2)2(tmtacn)2]2+, which show remarkable redox and solvent-dependent coordination chemistry, are the resting state of the catalytic system and that they retain a dinuclear structure throughout the catalytic cycle. The mechanistic understanding obtained from these studies holds considerable implications for both homogeneous manganese oxidation catalysis and in understanding related biological systems such as dinuclear catalase and arginase enzymes.

CCDC 276369: Experimental Crystal Structure Determination

Related Article: J.W.de Boer, J.Brinksma, W.R.Browne, A.Meetsma, P.L.Alsters, R.Hage, B.L.Feringa|2005|J.Am.Chem.Soc.|127|7990|doi:10.1021/ja050990u,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 276368: Experimental Crystal Structure Determination

Related Article: J.W.de Boer, J.Brinksma, W.R.Browne, A.Meetsma, P.L.Alsters, R.Hage, B.L.Feringa|2005|J.Am.Chem.Soc.|127|7990|doi:10.1021/ja050990u,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.